When turbine engines are over-stressed by operating them at excessive power levels for excessive periods of time, early overhaul of the engines may be required. The complete overhaul of a tubine engine is a very expensive proposition, and for many aircraft can cost from $50,000 to $100,000.
Although maximum rated power for a turbine engine is normally only needed for a few minutes during take-off, some pilots, through carelessness or otherwise, may continue to use maximum power for a substantially longer period of time. This will cause overheating and overstressing of the engine and may result in the need for overhaul after much shorter periods of usage than would normally be required. Under these circumstances, operating costs for the aircraft are greatly increased.
It is also noted that turbine aircraft generally, and turbo-fan engines in particular, have certain maximum rated speeds for the fan section, for example, which are dependent upon altitude and air temperature, in addition to their dependence on the operation of auxiliary equipment such as de-icers. Individual aircraft may have a "map" indicating the maximum allowable RPM, as a function of the air pressure, and also of the air temperature. These characteristics may have a positive slope with increasing temperatures up to a predetermined maximum, and then a negative slope at higher temperatures. The foregoing constitutes an important aspect of the invention as described in my co-pending U.S. patent application Ser. No. 334,552, filed Dec. 23, 1981.
In my U.S. Pat. No. 4,185,460, granted Jan. 29, 1980, I disclosed a push-button power control system wherein pushbuttons were provided to set power levels for "take-off", for "climb", for cruising and for landing "approach" speeds. These pushbuttons were to be mounted on the pilot hand wheel for ease and convenience in pilot operation. However, in the system of U.S. Pat. No. 4,185,460, in continuing actuation of the "take-off" pushbutton, the pilot could continue to operate the plane under maximum power conditions for prolonged periods of time, and thereby overheat and overstress the turbine engines.
A principal object of the present invention is to avoid turbine damage of the type outlined above, and to reduce aircraft maintenance costs by avoiding stressful engine operating conditions.